The use of electrical connectors to removably couple electrical or electronic components, cables or wires is well known in the art. A feature common to almost all electrical connectors is the use of conductive contacts to establish electrical conductivity. Conductive contacts are typically fabricated from base metal, e.g.: copper or brass. In order for low-loss electrical conductivity to be established between two metallic contacts which are not soldered or otherwise rigidly connected, the contacts must be firmly held together. The presence of any non-conductive material between a pair of contacts tends to reduce or eliminate their electrical conductivity.
A problem common to the manufacture of electrical contacts is that the material frequently used for such contacts generates, through chemical action, corrosion products which inhibit or prevent electrical conductivity. For instance, copper contacts which are exposed to atmospheric sulfur tend to form cuprous or cupric sulfates. The process of forming these copper sulfates reduces conductivity between the contacts in several ways. First, these corrosion products themselves tend to be poor conductors of electricity. Second, the process of the chemical formation of these corrosion salts pits and corrodes the surface of the two contacts thereby reducing the surface area available for contact and maximized transfer of electrons. Finally, a corrosion product interposed between mating electrical contacts act as an abrasive and tend to increase the physical separation, and hence the resistance of those contacts to electrical flow.
While the preceding discussion has used copper contacts as an example, the same problem exists, to a greater or lesser degree, with most metallic contacts. The problem is aggravated when the contacts are formed of different metals having different electrode potentials. As is well known, contact between two such dissimilar metallic contacts, particularly in the presence of a substance acting as an electrolyte, results in some degree of bimetallic corrosion.
The high power typically encountered in some electrical applications, electrical power transmission equipment for instance, tends to overcome imperfections in electrical contacts. Furthermore, power transmission connectors are generally subjected to relatively few connect/disconnect cycles during their life span. For these reasons, as well as cost considerations, many electrical contacts are fabricated from base metal and utilize a sliding compression to effect connectivity. Contact corrosion and erosion is a significant problem however, in the electronic arts where low power applications are common. A low power electronic signal is especially susceptible to signal loss due to contact corrosion. For all the previously discussed reasons, it is standard practice in applications requiring a high degree of electrical reliability and low signal loss, to plate the respective electrical contact pairs with a metal which is resistant to corrosion. One well known such metal is gold.
Pure gold is a relatively dense, soft metal and is an excellent conductor of electricity. In its unalloyed state, gold tends to abrade easily. Due to many factors, not the least of which is the cost of gold, the thickness of gold plating for electrical contacts is typically in the range of 50 millionths of an inch (50/1,000,000"). Gold plating of this thickness is sufficient to ensure near perfect electrical conductivity when electrical contacts are newly plated. Furthermore, the presence of such gold plating over a base metal contact pair significantly reduces the vulnerability of the substrate base metal to oxidative, corrosive or bimetallic attack.
The need for gold-plated high-reliability electrical contacts was highlighted in a recent Congressional probe. Dr. Puckett, the General Manager of Hughes Aircraft Co., was called in front of a Congressional committee investigating defense contractor charges. One of the senators asked, "Dr. Puckett, Hughes is well-known as the `Cadillac` of the defense industry. Can you explain to me why every one of the electrical contacts you sell the government has to be gold-plated?" Dr. Puckett replied, "Why, you know the answer to that question as well as I do, Senator. Gold plating electrical contacts is much cheaper than machining them out of solid gold."
As was previously discussed, it is necessary to maintain a contact pair in immediate contact to ensure a reliable, electrically conductive path. Prior art electrical connectors generally utilize some form of sliding or compressive friction to ensure the conductivity between two contacts. A commonplace example of a sliding friction contact is the ordinary 110 volt wall plug and mating lamp cord plug, wherein a pair of copper prongs are seated in a pair of spring loaded copper or copper alloy receptacles. The receptacles contain spring clips, or the like, which are pushed aside under friction as the prongs enter. While the sliding friction of the prongs (or plug) as they are pushed into the receptacles has the effect of removing insulating corrosive or oxidative products from the prongs and receptacles, it also produces some degree of wear. This design is perfectly adequate for typical household or light industrial service. However, such an unplated plug and receptacle pair generally yields an unacceptable level of signal loss when used in many electronic applications, particularly those with highly repetitive coupling/decoupling requirements. This signal loss therefore gives rise to the use of the gold plating previously discussed.
Efforts by other workers in the electrical and the electronic arts have yielded a plethora of electrical contact systems for general and specialized uses. Apparently all of them utilize some form of sliding or compression friction to establish and maintain electrical contact between connector elements. Representative examples of such electrical connector systems are found in the following U.S. Patents: U.S. Pat. No. 3,208,030 to Evans, et al.; No. 4,500,159 to Briones, et al.; No. 4,544,227 to Hirose; No. 4,602,838 to Davis, et al.; No. 5,035,639 to Kilpatrick, et al.; and No. 5,147,215 to Pritulsky. Each of the aforementioned prior art patents utilizes a sliding or friction contact system which aggravates the previously discussed wear problem.
The use of gold-plated contacts for high-fidelity or precision electronic components is not, however, without its faults. Not the least of which is the fact that gold, being a relatively soft metal, is very susceptible to the mechanical wear between contacts which is caused by coupling and decoupling a connector. This mechanical wear is aggravated by any form of abrasive material entrained between the mating contact pair, and eventually acts to remove the gold layer and expose the base metal substrate to the corrosive processes previously discussed. For many applications, gold-plating a contact pair which will mate with sliding friction is a perfectly adequate methodology. Commonly, in these applications the number of times a connector is coupled and uncoupled tends to be relatively low, so the cumulative effect on overall conductivity of abrasives, entrained between contact elements, is negligible.
In order to produce the intimate contact between contacts required for low-loss connectivity, one prior art methodology is to spring-load one rigid contact face to bias it toward another contact, also having a rigid face. However, rigid-faced contacts are limited to a fixed contact area unless friction mating is utilized which in turn introduces the mechanical wear problem previously discussed.
Some connectors, such as those used on headphones are connected and disconnected from their respective electronic devices many times per day. Examples of such headphone use include sonar sets, transcription machines, PBX switchboards and so forth. Connectors for use with headphones on these equipments must deliver a consistently high standard of conductivity while being coupled and decoupled many thousands of times, and present a significant design challenge.
A gold-plated, base metal contact pair which operates under the principal of rotating or sliding friction is generally incapable of delivering low-loss conductivity over many thousand coupling/decoupling cycles. This is due to mechanical wear caused by sliding friction, exacerbated by the abrasive effect of corrosion products, airborne contaminants, and dust on the gold plating. Such frequency of coupling and decoupling tends to remove sufficient gold plating from the contacts that the previously discussed signal loss problem returns.
An electrical connector capable of being connected and disconnected without appreciable sliding friction, and attendant wear between the corresponding contacts thereof, would obviate the abrasion problem which shortens the life of high couple/decouple cycle connectors. Such a connector would provide significant advantages in reliability and life span.